Spreadsheet Modeling
To solve optimization problems with Gnumeric you have to type in the problem into a sheet. A recommended way to start with is to allocate a separate column in the spreadsheet for each decision variable (in the previous example the x, y, and z) and a separate row for each constraint (the constraints #1-#4). The coefficients of these variables should be placed into the cells corresponding to the allocated row and the column. It is also recommended that you label the rows and the columns to make the sheet much more readable. The sheet for our maximization problem would look like this:
As you can see, we have put the model variables into cells B3:D3. They are currently all zeros. The cell E4 contains the objective function definition. The easiest way to define it is to use SUMPRODUCT build-in function. Thus in our model, we have the formula `=SUMPRODUCT(B3:D3,B4:D4)' in E3.
The constraints are defined in rows seven to ten. Since the coefficients of these functions are in columns B, C and D we will get the total sum of each of the constraint using the formula `SUMPRODUCT(B$3:D$3,Bn:Dn)' where n is the row number of the constraint. For example, in E7 we have `=SUMPRODUCT(B$3:D$3,B7:D7)', in E8 `=SUMPRODUCT(B$3:D$3,B8:D8)' and so on. The right hand side (RHS) values of the constraints are typed into cells G7:G10.